Process for making steel insensible to the action of hot gases and vapors



Patented Oct. 27, 1931 UNITED STATES PATENT OFFICE BEN'NO STRAUSS, OFISSEN, GERMANY, ASSIGNOR TO FRIED. KRUPP AKTIENGESEL L- SGHAFT, FESSENON-THE-RUHR, GERMANY PROCESS FOR MAKING STEEL INSENSIBLE TO THEACTION OF HOT GASES AND VAPOBS Ho Drawing. Application filed November18, 1926,

Steel when exposed to the action of hot gases and vapors generallybecomes brittle, this brittleness, in its turn, causing cracking of thesteel. for instance with steam boilers and high pressure receptacles.The tendency to crack is greater, the higher the pressure to which thearticles are exposed dur' ing operation. The change in the texturetaking place due to the action of hot gases and vapors consists in anenlargementof the grain boundaries which are in a. yieldingly tensionedcondition, and in phenomena arising in the grain boundaries which havenot been explored hitherto. Probably these phenomena consist in thereaction of certain constituents of the steel with the gases. In steamboilers, for instance, the products of dissociation of the water,hydrogen and oxygen, cause such a reaction, the oxygen in particulartending to enlarge the grain boundarie's, when in nascent state. For,the grain boundaries which are to be considered the seat of the oxidesenveloping the individual grains as closed pellicles so to speak, formways for the entrance of gases and vapors, the penetrating gases andvapors. in their turn, cause a noxious alteration of the cohe'renceprevailing between the individual crystal grains and thus generate asuccessively increasing brittleness which may be denoted as aging of thematerial.

Now my invention has for its object to provide a proces which willprevent the hot gases and vapors from exerting a noxious effect on thesteel or the articles made thereof. This object is obtained according tomy invention by subjecting the steel or the articles made thereof to aheat treatment by which the grains and the oxide particles lying betweenthem are refined to such an extent that grain boundaries can no longerbe detected.

In carrying out the process forming the subject-matter of my invention,preferably a steel is made use of containing for instance about to 4 percent of nickel, to 2 per cent of chromium and 0.1 to 0.39 per cent ofcarbon, thisbeing a steel in which a formation of martensite takes placewhen quickly I. cooled from above the pointof recalescence,

Serial No. 149,282, and in Germany April 1, 1926.

A03, in the present example from 900 C., and in which by a subsequentreheating, in the present example up to about 600 to 650 C., the desiredproperties of strength are obtaincd, without grain boundaries beingformed again or an alteration of the distribution of the oxides arisingotherwise.

When a steel of this nature is treated in the indicated manner, grainboundaries can no longer be detected by an etching test. The steel hasthus been brought into a condition of highest tenacity in which apenetration of hot gases and vapors is excluded and which does notundergo any subsequent alteration.

Besides chromium and nickel, silicon vanadium and tungsten come intoconsideration as additions, the percentage of the additions depending onthe cross sections of the articles to be manufactured of the steel.

Having now described my invention, what I claim as new and desire tosecure by Letters Patent, is

1. The process of treatin steel containing about A,, to 4 per cent 0nickel, to 2 per cent of chromium and 0.1 to 0.39 per cent of carbon torender the same insensible to the action of hot gases and Vapors, whichconsists in refining the grains and the oxide particles lying betweenthem by heating the steel above the point of recalescence, AC3, quicklycooling it from above this point and reheating it up to about 600 to 650C.

2. The process of treating steel containing about V; to 4 per cent ofnickel, to 2 per cent of chromium, 0.1 to 0.39 per cent of carbon, andto render the same insensible to the action of hot gases and vapors,which consists in refining the grains and the oxide particles lyingbetween them by heating the steel above the point of recalescence, A03,quickly cooling it from above this paint and reheating it up to about600 to 650 w 3. The process of treating steel containing about to 4 percent of nickel, to 2 per cent of chromium and 0.1 to 0.3 per cent ofcarbon to render the same insensihle to the action of hot gases andvapors, which consists in refining thegrains and the oxide 100 particleslying between them by heating the steel above the point of recalescenceA03, quickly cooling it from above this point and reheating it up toabout 600 to 650 C.

4. An iron alloy containing to 4% of nickel, A), to'2% of chromium, and0.1 to 0.39% of carbon and heat treated according to the processdescribed in claim 1, said alloy having high tenacity and resistance tocorrosion by hot gases and vapors and having a structure which appearsin an etched section as a continuous mass unbroken by grain boundaries.

5. An iron alloy containing to 4% of nickel, to 2% of chromium, 0.1 to0.39%

of carbon, and tungsten, and heat treated according to the processdescribed in claim 2,

said alloy having high tenacity and resistance to corrosion by hot gasesand vapors and having a structure which appears in an etched section asa continuous mass unbroken by grain boundaries.

The foregoing specification signed at Colggne, Germany, this 26th day ofOctober,

BENNO STRAUSS.

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